A source with knowledge of the lease said that Appssavvy took about 10,000 square feet on the second floor of the roughly 210,000 square foot building. Asking rents at the property are in the mid $40s per square foot.

594 Broadway

A spokesman for Appssavvy, Steve Stratz, confirmed the deal, saying the firm had grown from a two-man operation in 2008 to about 50 employees today. He said the firm plans to grow to about 65 people in the next space.

The company is part of a wave of fast growth and success – not to mention leasing – among tech and new media firms, particularly in the Midtown South office neighborhood.

Appssavvy specializes in creating online advertisements that more seamlessly integrate with the websites where they are displayed.

“People are conditioned to look away from banner ads and ads on the side of a webpage,” Mr. Stratz explained. “If you were sending an email, let’s say, Appssavvy would build the ad into a confirmation box that would come up when you sent the email. It’s much more connected to what the user is doing.”

Appssavvy was represented in the deal by Gregory Kraut, an executive who is the head of the Canadian brokerage company Avison Young’s recently-launched New York branch. Mr. Kraut, who was a broker at CBRE before leaving last year to join Avison Young, couldn’t be reached for comment.

Donna Vogel, a broker at Newmark Grubb Knight Frank, was the agency representative in the deal. The building is part of a portfolio owned by Newmark’s original partners, including Jeff Gural.